[1] Univ Oslo, Inst Clin Dent, Dept Periodontol, Pb 1109 Blindern, N-0317 Oslo, Norway
[2] Sapienza Univ Rome, Sect Periodontol, Dept Dent & Maxillofacial Sci, Rome, Italy
[3] Jonkoping Univ, Sch Hlth Sci, Dept Nat Sci & Biomed, Ctr Oral Hlth, Jonkoping, Sweden
[4] Publ Dent Hlth Serv, Dept Periodontol, Kristianstad, Sweden
[5] Queen Mary Univ London, Ctr Primary Care & Publ Hlth, London, England
[6] Publ Specialist Dent Clin, Dept Periodontol, Karlskrona, Sweden